Nicotine, which is the major psychoactive constituent of tobacco, is one of the most widely used substances of abuse. In recent years it has become well established that the mechanism of action of nicotine on the central nervous system is mediated via nicotinic receptors which are distinct from those at the neuromuscular junction and appear to exist in multiple subtypes. The overall objective of this proposal is aimed at the molecular characterization of brain sites for nicotine action. 1) Purification of the brain nicotinic receptor proteins by affinity and immunoaffinity chromatography. Amino acid sequence will be performed on the 55 and 62 kdalton proteins which are believed to be associated with the nicotinic recognition sites. 2) Structure- activity studies with newly synthesized nicotinic agonists and antagonists. Additional carbamate and heterocyclic carboxylic acid esters of alkylaminoalkyl alcohols will be synthesized and tested pharmacologically and for receptor binding. They will be tested for their ability to block the central and peripheral effects of nicotine. 3) Structure-activity studies with bridged analogues of nicotine. The compounds will be screened for their psychotropic and cardiovascular effects as well as for 3H-nicotine and (3)H-methylcarbamylcholine binding. 4) Studies aimed at determining the mode of mecamylamine's antagonism to nicotine. Characterization and purification of the mecamylamine binding site in rat brain; a site which is believed to be associated with an ionic channel. A polyclonal anti-idiotypic antibody for mecamylamine will be prepared for purification of the mecamylamine binding site by immunoaffinity chromatography. 5) Characterization and identification of the nicotinic receptor by affinity labeling. A number of high specific activity radiolabeled affinity ligands of nicotine will be synthesized and used to label the nicotine receptor proteins. Such studies should contribute a better understanding of the chemical and psychopharmacologic nature of nicotine's action; and it is hoped that the structure-activity studies with novel agonists and antagonists may result in the development of drugs for the treatment of the tobacco habit as well as memory disorders, such as senile dementia.